Catalyst system, process for olefin polymerization, and polymer compositions produced therefrom

Abstract

Provided are catalyst systems, processes for polymerizing one or more olefins, polymers resulting therefrom, and articles prepared from such polymers. The processes comprise contacting under polymerization conditions one or more olefin monomers, preferably propylene, with a catalyst system comprising a transition metal compound and an activator of the formula (1) or (2) as described herein. The polymer compositions described herein exhibit advantageously narrow composition distributions and high melting points in comparison to conventional polymers having the same comonomer content. The polymers described herein exhibit improved properties, e.g., pellet stability, impact properties, heat seal properties, and structural integrity in film and fabricated parts applications.

We claim: 
     
       1. A copolymer composition comprising units derived from propylene and ethylene, where the copolymer comprises from about 0.1 to about 20 wt % units derived from ethylene, and:
 i. the density of the copolymer composition is less than about 0.970 g/cc, 
 ii. the heat of fusion of the copolymer composition is less than about 75 J/g, 
 iii. the melting point of the composition satisfies the relation T m >−6.2*e+125, where e is the ethylene content of the composition in wt % and Tm is the melting point in degrees Celsius, 
 iv. the copolymer is prepared using one or more metallocene catalysts, and 
 v. the copolymer composition has a T 75 −T 25  value of less than 20, where T 25  is the temperature in degrees Celsius at which 25% of the eluted polymer is obtained and T 75  is the temperature in degrees Celsius at which 75% of the eluted polymer is obtained via temperature rising elution fractionation (TREF). 
 
     
     
       2. The copolymer composition of  claim 1 , wherein the copolymer comprises from about 2 to about 20 wt % units derived from ethylene. 
     
     
       3. The copolymer composition of  claim 2 , wherein the composition comprises from about 3 to about 16 wt % units derived from ethylene. 
     
     
       4. The copolymer composition of  claim 3 , wherein the composition comprises from about 5 to about 14 wt % units derived from ethylene. 
     
     
       5. The copolymer composition of  claim 1 , wherein the density of the composition is less than about 0.940 g/cc. 
     
     
       6. The copolymer composition of  claim 5 , wherein the density of the composition is from about 0.860 to about 0.900 g/cc. 
     
     
       7. The copolymer composition of  claim 1 , wherein the molecular weight of the copolymer is from about 20,000 to about 400,000 g/mol. 
     
     
       8. The copolymer composition of  claim 1 , wherein the molecular weight distribution of the copolymer is from about 2.0 to about 2.4. 
     
     
       9. The copolymer composition of  claim 1 , wherein the soluble fraction, F a , of the copolymer satisfies the following relation:
     F   a <7 *e+ 35, 
 where e is the ethylene content of the composition in wt %, 
 
       where the soluble fraction, Fa, is measured at −15° C. in a solution of orthodichlorbenzene. 
     
     
       10. The copolymer composition of  claim 1 , wherein the soluble fraction, F a , of the copolymer satisfies the following relation:
     F   a <7 *e+ 38, 
 where e is the ethylene content of the composition in wt %, 
 
       where the soluble fraction, Fa, is measured at −15° C. in a solution of orthodichlorbenzene. 
     
     
       11. The copolymer composition of  claim 1 , wherein the soluble fraction, F a , of the copolymer satisfies the following relation:
     F   a <7 *e+ 40, 
 where e is the ethylene content of the composition in wt %, 
 
       where the soluble fraction, Fa, is measured at −15° C. in a solution of orthodichlorbenzene. 
     
     
       12. An article comprising the copolymer composition of  claim 1 . 
     
     
       13. The article of  claim 12 , where the article is a film, fiber, nonwoven fabric, or molded article. 
     
     
       14. A polymer pellet comprising the copolymer composition of  claim 1 .